<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>


</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="fn(1)">
<input type="button" value="减" onclick="fn(2)">
<input type="button" value="乘" onclick="fn(3)">
<input type="button" value="除" onclick="fn(4)">
<div>结果：0</div>

<script>
    // 获取两个文本框
    let i=document.querySelector("#i1");
    let j=document.querySelector("#i2");
    let d=document.querySelector("div");
    function fn(x) {
        if(isNaN(i.value)||isNaN(j.value)){
            d.innerText="输入错误";
            return;
        }
        switch (x) {
            case 1: d.innerText="结果："+(parseFloat(i.value)+parseFloat(j.value));break;
            case 2: d.innerText="结果："+(parseFloat(i.value)-parseFloat(j.value));break;
            case 3: d.innerText="结果："+(parseFloat(i.value)*parseFloat(j.value));break;
            case 4: d.innerText="结果："+(parseFloat(i.value)/parseFloat(j.value));break;
        }

    }
</script>

</body>
</html>